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2018, Journal of Scientific Computing
In this paper, a shape optimization problem corresponding to the p-Laplacian operator is studied. Given a density function in a rearrangement class generated by a step function, find the density such that the principal eigenvalue is as small as possible. Considering a membrane of known fixed mass and with fixed boundary of prescribed shape consisting of two different materials, our results determine the way to distribute these materials such that the basic frequency of the membrane is minimal. We obtain some qualitative aspects of the optimizer and then we determine nearly optimal sets which are approximations of the minimizer for specific ranges of parameters values. A numerical algorithm is proposed to derive the optimal shape and it is proved that the numerical procedure converges to a local minimizer. Numerical illustrations are provided for different domains to show the efficiency and practical suitability of our approach.
We consider a multiphase shape optimization problem in relation to the eigenvalues of the Dirichlet Laplacian. We give some new results concerning the qualitative properties of the optimal sets and the regularity of the corresponding eigenfunctions. We also provide numerical results for the optimal multiphase configurations.
2019
In this work we study the geometric shape optimization of membrane in the presence of a diffusion field of molecules, such as proteins which have the ability to adsorb on, and to desorb from the membrane. The main idea of this study is to vary the position of the boundaries of a given initial shape of the membrane, without changing its topology which remains the same as the initial shape. We develop a model that includes, molecular diffusion along the membrane as well as the attachment and detachment of molecules to and from the membrane. The numerical simulations based on Level-Set method show that the coupling between the membrane and the molecules makes the membrane suffer from morphological instability.
Mathematical Methods in the Applied Sciences, 2009
We give an overview of results on shape optimization for low eigenvalues of the Laplacian on bounded planar domains with Neumann and Steklov boundary conditions. These results share a common feature: they are proved using methods of complex analysis. In particular, we present modernized proofs of the classical inequalities due to Szegö and Weinstock for the first nonzero Neumann and Steklov eigenvalues. We also extend the inequality for the second nonzero Neumann eigenvalue, obtained recently by Nadirashvili and the authors, to nonhomogeneous membranes with log‐subharmonic densities. In the homogeneous case, we show that this inequality is strict, which implies that the maximum of the second nonzero Neumann eigenvalue is not attained in the class of simply connected membranes of a given mass. The same is true for the second nonzero Steklov eigenvalue, as follows from our results on the Hersch–Payne–Schiffer inequalities. Copyright © 2009 John Wiley & Sons, Ltd.
We investigate numerically a 1956 conjecture of Payne, Polya, and Weinberger. The conjecture asserts that the ratio of the first two eigenvalues of the Laplacian on a bounded domainOmega of the plane with Dirichlet boundary conditions reaches its minimum value precisely whenOmega is a disk. A crucial feature of this problem is the loss of smoothness of the objective function at the solution. The following results form the core of our numerical treatment. First, we construct finite dimensional families of deformations of a disk equipped with a uniform triangulation. This permits the formulation of a discrete model of the problem via finite element techniques. Second, we build on the work of M. Overton to derive optimality conditions in terms of Clarke's generalized gradients for nonsmooth functions. These ideas are then combined into an algorithm and implemented in Fortran. Contents 1 Introduction 2 2 Preliminaries 4 3 Max characterization of P k i=1 i for symmetric matrices 8 4 ...
It is known that the torsional rigidity for a punctured ball, with the puncture having the shape of a ball, is minimum when the balls are concentric and the first eigenvalue for the Dirichlet Laplacian for such domains is also a maximum in this case. These results have been obtained by Ashbaugh and Chatelain (private communication), Harrell et. al., by Kesavan and, by Ramm and Shivakumar. In this paper we extend these results to the case of $p$-Laplacian for $1 < p < \infty$. For proving these results, we follow the same line of ideas as in the aforementioned articles, namely, study the sign of the shape derivative using the moving plane method and comparison principles. In the process, we obtain some interesting new side results such as the Hadamard perturbation formula for the torsional rigidity functional for the Dirichlet $p$-Laplacian, the existence and uniqueness result for a nonlinear pde and some extensions of known comparison results for nonlinear pdes.
Applied and Computational Mathematics, 2021
The fractional Laplacian is a nonlocal operator that appears in biology, in physic, in fluids dynamic, in financial mathematics and probability. This paper deals with shape optimization problem associated to the fractional laplacian ∆ s , 0 < s < 1. We focus on functional of the form J(Ω) = j(Ω, u Ω) where u Ω is solution to the fractional laplacian. A brief review of results related to fractional laplacian and fractional Sobolev spaces are first given. By a variational approach, we show the existence of a weak solution u Ω belonging to the fractional Sobolev spaces D s,2 (Ω) of the boundary value problem considered. Then, we study the existence of an optimal shape of the functional J(Ω) on the class of admissible sets O under constraints volume. Finally, shape derivative of the functional is established by using Hadamard formula's and an optimality condition is also given.
2009
The goal of the topological optimization problem is to find an optimal design with an a priori poor information on the optimal shape of the structure. The shape optimization problem consists in minimizing a functional j Ω J Ω, uΩ where the function uΩ is defined, for example, on a variable open and bounded subset Ω of R. For ε > 0, let Ωε Ω \ x0 εω be the set obtained by removing a small part x0 εω from Ω, where x0 ∈ Ω and ω ⊂ R is a fixed open and bounded subset containing the origin. Then, using general adjoint method, an asymptotic expansion of the function will be obtained in the following form:
Computational Optimization and Applications, 2020
This paper is devoted to a numerical method for the approximation of a class of free boundary problems of Bernoulli's type, reformulated as optimal shape design problems with appropriate shape functionals. We show the existence of the shape derivative of the cost functional on a class of admissible domains and compute its shape derivative by using the formula proposed in [6, 7], that is, by means of support functions. On the numerical level, this allows us to avoid the tedious computations of the method based on vector fields. A gradient method combined with boundary element method are performed for the approximation of this problem, in order to overcome the re-meshing task required by the finite element method. Finally, we present some numerical results and simulations concerning practical applications, showing the effectiveness of the proposed approach.
2006
This paper concerns an optimization problem related to the Poisson equation for the p-Laplace operator, subject to homogeneous Dirichlet boundary conditions. Physically the Poisson equation models, for example, the deformation of a nonlinear elastic membrane which is fixed along the boundary, under load. A particular situation where the load is represented by a characteristic function is investigated.
Communications in Nonlinear Science and Numerical Simulation, 2011
In this paper numerical approximation for the m-membrane problem is considered. We make a change of variables that leads to a different expression of the quadratic functional that allows after discretizing the problem to reformulate it as finite dimensional bound constrained quadratic problem. To our knowledge this is the first paper on numerical approximation of the m-membrane problem. We reformulate the m-membrane problem as a bound constraint quadratic minimization problem. The bound constraint quadratic form is solved with the gradient projection method.► We describe numerical approximation for the m-membranes problem. ► The original m-membranes problem is equivalent to the functional’s minimization over the same set. ► The problem expressed in displacements u can be reformulated in terms of u-differences. ► The finite dimensional version of bound constrained minimization problem written as a quadratic form. ► This problem can be solved with different methods, for numerical experiments gradient projection method is used.
Structural and Multidisciplinary Optimization, 2009
We consider a shape optimization problem of finding the optimal damping set of a two-dimensional membrane such that the energy of the membrane is minimized at some fixed end time. Traditional shape optimization is based on sensitivities of the cost functional with respect to small boundary variations of the shapes. We use an iterative shape optimization scheme based on level set methods and the gradient descent algorithm to solve the problem and present numerical results. The methods presented allow for certain topological changes in the optimized shapes. These changes can be realized in the presence of a force term in the level set equation. It is also observed that the gradient descent algorithm on the manifold of shapes does not require an exact line search to converge and that it is sufficient to perform heuristic line searches that do not evaluate the cost functional being minimized.
We consider a model problem of isogeometric shape optimization of vibrating membranes whose shapes are allowed to vary freely. The main obstacle we face is the need for robust and inexpensive extension of a B-spline parametrization from the boundary of a domain onto its interior, a task which has to be performed in every optimization iteration. We experiment with two numerical methods (one is based on the idea of constructing a quasi-conformal mapping, whereas the other is based on a spring-based mesh model) for carrying out this task, which turn out to work sufficiently well in the present situation. We perform a number of numerical experiments with our isogeometric shape optimization algorithm and present smooth, optimized membrane shapes. Our conclusion is that isogeometric analysis fits well with shape optimization.
ZAMM, 2006
We consider a general formulation for shape optimization problems involving the eigenvalues of the Laplace operator. Both the cases of Dirichlet and Neumann conditions on the free boundary are studied. We survey the most recent results concerning the existence of optimal domains, and list some conjectures and open problems. Some open problems are supported by efficient numerical computations.
Communications in Mathematical Physics, 2000
We consider the following eigenvalue optimization problem: Given a bounded domain Ω ⊂ R n and numbers α ≥ 0, A ∈ [0, |Ω|], find a subset D ⊂ Ω of area A for which the first Dirichlet eigenvalue of the operator −∆ + αχD is as small as possible.
Comptes Rendus Mécanique, 2005
A shape optimization problem is considered for the Dirichlet Laplacian. Asymptotic analysis is used in order to characterise the optimal shapes which are finally given by a singular perturbation of the smooth initial domain. To cite this article: S.A. Nazarov, J. Sokolowski, C. R. Mecanique 333 (2005). 2005 Académie des sciences. Published by Elsevier SAS. All rights reserved.
2009
In this article we deal with the problem of distributing two conducting materials in a given domain, with their proportions being fixed, so as to minimize the first eigenvalue of a Dirichlet operator. When the design region is a ball, it is known that there is an optimal distribution of materials which does not involve the mixing of the materials. However, the optimal configuration even in this simple case is not known. As a step in the resolution of this problem, in this paper, we develop the shape derivative analysis for this two-phase eigenvalue problem in a general domain. We also obtain a formula for the shape derivative in the form of a boundary integral and obtain a simple expression for it in the case of a ball. We then present some numerical calculations to support our conjecture that the optimal distribution in a ball should consist in putting the material with higher conductivity in a concentric ball at the centre.
Contemporary Mathematics, 2000
In this paper, continuing our earlier article [CGIKO], we study qualitative properties of solutions of a certain eigenvalue optimization problem. Especially we focus on the study of the free boundary of our optimal solutions on general domains.
ESAIM: Control, Optimisation and Calculus of Variations, 2013
Our concern is the computation of optimal shapes in problems involving (−Δ) 1/2. We focus on the energy J(Ω) associated to the solution uΩ of the basic Dirichlet problem (−Δ) 1/2 uΩ = 1 in Ω, u = 0 in Ω c. We show that regular minimizers Ω of this energy under a volume constraint are disks. Our proof goes through the explicit computation of the shape derivative (that seems to be completely new in the fractional context), and a refined adaptation of the moving plane method.
Computer Methods in Applied Mechanics and Engineering, 2009
This paper deals with the development of a discretization strategy that minimizes the total computing time for solving shape optimization problems in linearly elastic systems. It employs a combination of boundary elements for integration of the governing differential equations and a first-order optimization algorithm. The proposed optimal discretization strategy is implemented and tested using a representative example problem and its effectiveness is assessed in comparison to alternative strategies.
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